Alpers syndrome (AS) is a mitochondrial disease that results in multi-organ defects, including neurodegeneration, epilepsy, liver failure, pancreatitis and gastrointestinal dysfunction. While mutations in the mitochondrial DNA replicase, polymerase-gamma (POLG) complex have been associated with AS in some patients, genetic causes of AS in most patients remain unknown. In order to determine mechanisms of disease progression in vivo and to develop effective treatments for AS, it is essential to have a relevant animal model. Unfortunately, because knockout of the POLG genes leads to embryonic lethal phenotypes of knockout mice, there are no animal models recapitulating AS. The zebrafish is an outstanding vertebrate model owing to the feasibility of studying genetic disorders; further, many mutants have been described that recapitulate human diseases. Recently, a missense mutation in mitochondrial asparaginyl-tRNA synthetase (NARS2) has been found to be the causative genetic defect in a patient with Alpers syndrome (AS). Further, in a forward genetic screen to identify mutations causing post-developmental liver disease in zebrafish, we identified the same (nars2) mutant, which appears to closely recapitulate the liver phenotype found in AS. Indeed, our preliminary results show that the zebrafish nars2 mutant strikingly recapitulates various pathological defects observed in AS patients. In addition, valproic acid induced liver mitotoxicity in AS patients suggests that mitochondrial defects might be important in disease pathogenesis of AS. These findings have led us to hypothesize that 1) the nars2 mutant zebrafish recapitulates many features found in human AS; 2) the nars2 mutation results in increased susceptibility to drug induced hepatic mitotoxicity and 3) inhibition of mitochondrial permeability transition pore (mPTP) opening will ameliorate the nars2 mutant phenotype. Therefore, in Aim 1, we will characterize the full range of pathophysiological abnormalities in the nars2 mutant, including extensive morphological characterization as well as mitochondrial functional assessment in live larvae.
In Aim 2, we will determine the susceptibility of nars2 mutant to drug induced liver injury and in addition, we will explore mPTP inhibitors as a novel therapy for AS. We propose that successful completion of these Aims will establish the first animal model of AS and in addition, identify novel therapies fo AS. The work will add substantially to the body of literature in AS, and will serve as the foundation for an R01 application to determine common and critical signaling pathways by comparing other mitochondrial diseases.
Public Health Relevance/Narrative This project directly addresses human health through the study of the first animal model of Alpers syndrome (AS), a mitochondrial disease that causes premature death in children due to brain and liver injury. Our novel zebrafish model of AS will not only bring new mechanistic insights to this disease, but it may also identify novel treatment of AS (for which no treatment currently exists).
| Chan, Sherine S L (2017) Inherited mitochondrial genomic instability and chemical exposures. Toxicology 391:75-83 |
